Properties of a toner are influenced by the materials and amounts of the materials of the toner. The charging characteristics of a toner also can depend on the carrier used in a developer composition, including, the carrier coating.
Toners having triboelectric charge within the range of about −30 μC/g to about −45 μC/g may be achieved by including smaller-sized silica particles as external additives, for example, silica particles having average sizes of less than about 20 nm, such as, for example, R805 (˜12 nm) and/or R972 (˜16 nm) (Evonik, NJ). However, developability at areas of low toner area coverage degrades over time. That has been attributed to the smaller-sized additives being impacted into the toner surface over time.
The problem with smaller-sized additives may be addressed by using larger-sized additives, i.e., additives having a size of about 40 nm or larger such as, for example, RX50 silica, RX515H silica or SMTS 103 titania (Evonik, NJ). However, such toners do not exhibit as high a triboelectric charge and also exhibit charge through.
New carrier coatings are being developed that enable higher charge developers, particularly those with larger-sized additive packages. However, when such developers are tested at low area coverage followed by high area coverage, the developers tend to exhibit low or wrong sign toner due to charge through, i.e., the incumbent toner in the device becomes less negative or even of the wrong sign, that is, the opposite charge, i.e., positive, and the new (fresh) toner added may charge very negative. The presence of low charge and/or wrong sign toner can result in objectionable background.
There remain problems with providing high charge with good relative humidity (RH) sensitivity of charge to changing environmental conditions for carrier coating resin designs. For example, there remains a need to tune the charge of the carrier resin to produce higher toner charge.
Further, many toners contain silica as a surface additive. Silica can be a substantial charge driver for a toner, although silica is known to be RH sensitive. Hence, it is a goal to provide new carrier designs that work well with silica to improve RH sensitivity, while maintaining high charge.